The invention relates to a filler for a surface-treatment composition, in particular to a wood-treatment composition. The invention further relates to the use of particles having a surface coating which gives each particle a positive surface charge, for treating wood.
Various surface-treatment compositions are known from the prior art. In this case, they can be for example lacquers, glazes, impregnations, coatings, stains, anodisation, powder coatings, galvanic metal deposits, oxidation (e.g. anodisation) and others. For some of the methods mentioned, it is known that the surface treatment can also have negative properties in terms of the appearance and/or properties of the treated material. An example of this is the application of lacquers to specific surfaces, since for example depending on the material to be coated, said material may be damaged as a result of the solvent contained in the lacquer.
In the case of surface-treatment compositions, which are intended to give the material to be treated a specific colour, negative interactions between the material itself and the surface-treatment composition are likewise known. These interactions can lead for example to components from the material ending up in the surface-treatment composition which change the appearance of the surface since either they are themselves coloured and can be perceived by their own colour or they change the shade of the pigments which may be contained in a surface-treatment composition and thus can be perceived as a change in colour. Since many dyes are characterised by a conjugated π-electron system and this can be greatly affected by interactions with electric charges or electric partial charges, in particular the diffusion of anions or cations from the surface-treated material into the surface coating is problematic. This is particularly noticeable in the case of what is known as bleeding (or bleed-through) of wood. The mostly ionic substances contained in the wood are generally water-soluble. As a result of the increased use of water-based solvent systems for modern paints, lacquers and other surface-treatment compositions, the wood substances are increasingly dissolved out by these and thus in particular in the water-based systems can interact with the surface coating. Since surface coatings based on organic solvents are increasingly being replaced, this so-called “bleed-through” is an increasingly occurring problem.
This problem does not occur to the same extent in all types of wood. Differences can be caused for example by the different wood substances of various types. The location and the growth conditions can also have an effect, since they can also affect the wood substances and the percentage distribution thereof. Softwoods usually differ from types of hardwood with respect to the tendency for bleed-through and also with respect to the escaping substances. In the case of types of hardwood, tropical woods in particular are very rich in wood substances which cause discolouration. Also in the case of wood portions from a single tree, bleed-through can occur locally to varying degrees. Bleed-through occurs more frequently in particular in the region of knotholes or knots, since at these points, the substances are particularly concentrated, the orientation of the capillaries promotes this, or the substances can escape more easily at these points for other reasons.
It is known from the prior art that in particular anionic components are relevant to the bleed-through of wood. Therefore, surface-treatment compositions for treating wood are commercially available which contain cationic binders which are intended to bind these anionic components from the wood when they escape from the wood. Such surface-treatment compositions are effective to a certain degree. However, it has become apparent that over time, as a result of the still possible mobility of the anions in the surface coating, a gradient appears in the anion concentration. Thus, the mentioned surface-treatment compositions bring about merely the reduction of locally occurring large concentrations of the anions of the wood substances, but cannot completely prevent the mobility thereof within a surface coating. Accordingly, local discolourations can thus be reduced, but this inevitably results in a slight change of colour in other regions.